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One more time - best way to tell gear ratio

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BurbinOR, Feb 17, 2001.

  1. BurbinOR

    BurbinOR 3/4 ton status

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    Have a one ton rear end (14BFF) that I am looking at tomorrow - guy thinks it is "3.73 or 3.88" ratio??????? Anyway, he admitted to knowing little to nothing about the gear ratios nor how to tell. They are in the truck currently, truck not running. Guess I should bring over my floor jack, then jack it up, mark the pinion, rotate the wheel one full revolution and see how many times the pinion turned. Correct?

    Or is counting the ring gear teeth, then the pinion gear teeth and doing the math a better idea? I want 4.10 ratio for the near future 35" tires.........

    Asking $250, thinks it has a "posi", which would be Gov-Lock, correct? Out of a '86 K30.

    <font color=orange>'79 - 406 TPI -<font color=orange> K5#5 - <font color=blue>See it at---&gt;<A target="_blank" HREF=http://www.blazzinor.coloradok5.com>http://www.blazzinor.coloradok5.com</A>
     
  2. Derf00

    Derf00 1/2 ton status

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    Frank,

    If you jack it up and turn the wheel, you have to do 2 revolutions of the tire. Doing the math would be more accurate, but you should be able to tell if it is 3.7?? or 4.??. If it turns out to be over 4, you might want to do the math to be exact.
     
  3. 90K5

    90K5 1/2 ton status

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    The ratio should be stamped on the ring gear so you won't have to count teeth.

    90K5

    See my truck at <A target="_blank" HREF=http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502>http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502</A>
     
  4. yeild2me

    yeild2me 1/2 ton status

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    yeah, go with what 90k5 said...it wont nessasarily be stamped like 4:10,,,but it will have the number of teeth on the ring and pinion on it i.e. 41 10 for 4:10's or 41 11 for 3:73's or something like that....its on there but its kinda small, but you will see it.....good luck....BTW mine has a posi in it and i could tell by the clutch packs...it may be a gov-lock, but i dont know what one looks like...i know that the gov-lock in my 10 bolt is very different than a posi, so its easy to tell, but i dont know what the 14 blt gov locks look like..........good luck

    AIRBORNE!!
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Pulling the cover is the best way. You'll find out the general condition of the diff, the numbers are stamped on the ring gear so you'll know ratio for sure too. You'll also find out if it is open or Gov-Lock as well. On a FF open is a 4 spider carrier and Gov-lock is a 3 spider carrier.
    You'll also get to see if the diff lube was changed reasonably often. If it was contaminated with water it'll be obvious.
    I don't think I'd ever buy a diff without pulling the cover off first. If I was selling a diff I wouldn't have any problems with removing the cover for inspection.
    86 K30? snag the front end while you're there dude! It'd be a Dana 60.
    By the way, the ratio should be 4.10 more than likely.

    Rene

    [​IMG]
    <P ID="edit"><FONT SIZE=-1>Edited by tRustyK5 on 02/17/01 05:37 PM (server time).</FONT></P>
     

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